I needed a solution that would display the center vertical and center horizontal gradients from JFreeChart in SVG.

As you rightly pointed out some months ago this is not straightforward. What I ended up doing was allowing JFreeChart to work with LinearGradientPaint and adding that as a supported gradient type in SVG. The implementation below only supports basic horizontal and vertical, but it works with any number of stops and colours.

Thanks for the feedback - I'd forgotten that LinearGradientPaint wasn't supported. I've fixed that for the upcoming 1.9 release and also improved the GradientPaint handling so that it will support the direction specified by the points on the GradientPaint. I'll get it released as soon as possible.